Degradable polyacrylonitrile-based carbon fiber as well as preparation method and application thereof

Abstract

The invention relates to degradable polyacrylonitrile-based carbon fibers as well as a preparation method and application thereof, and belongs to the technical field of carbon fiber manufacturing. The preparation method comprises the following steps: carrying out copolymerization reaction on acrylonitrile and an ester group-containing functional monomer to obtain a spinning solution; spinning the spinning solution to obtain a polyacrylonitrile precursor; sequentially carrying out pre-oxidation treatment and carbonization treatment on the polyacrylonitrile precursor, and carrying out surface activation treatment by adopting hydrogen peroxide, so as to obtain the degradable polyacrylonitrile-based carbon fiber. The preparation method comprises the following steps: copolymerizing acrylonitrile and an ester group-containing functional monomer, introducing a degradable ester bond into a polyacrylonitrile molecular chain, constructing a hydrolyzable breaking point, carrying out surface activation treatment by hydrogen peroxide after pyrolysis, etching the fiber surface to generate micropores, and selectively oxidizing the fiber surface to form a carboxyl group, so as to obtain the degradable polyacrylonitrile fiber. The prepared degradable polyacrylonitrile-based carbon fiber has the advantages of high strength, short degradation period and controllable degradation rate.

Description

Technical Field

[0001] This application relates to the field of carbon fiber manufacturing technology, and in particular to a biodegradable polyacrylonitrile-based carbon fiber, its preparation method and application. Background Technology

[0002] Carbon fiber possesses excellent mechanical properties, particularly high specific strength and specific modulus of elasticity, and is widely used as a reinforcing material in the aerospace, automotive, and leisure products industries. Furthermore, due to its superior mechanical properties, it can reduce the weight of aircraft, automobiles, and other vehicles, and is attracting widespread attention as a means of reducing carbon dioxide emissions in aircraft and automotive operating environments.

[0003] Traditional polyacrylonitrile (PAN)-based carbon fibers are difficult to degrade due to their highly graphitized structure (natural degradation takes hundreds of years), causing environmental pollution upon disposal; globally, over 400,000 tons of carbon fiber blades are discarded annually alone. Current biodegradable carbon fibers mostly use bio-based raw materials such as lignin and cellulose, resulting in low strength (tensile strength generally below 1.5 GPa), which fails to meet industrial demands and limits their applications. Therefore, current research focuses on modifying traditional carbon fibers to achieve biodegradability while maintaining strength, such as adding photosensitizers to the raw materials to achieve photodegradation. However, carbon fibers prepared in this way still suffer from long degradation cycles and uncontrollable degradation rates. Summary of the Invention

[0004] To address the aforementioned technical problems, the objective of this application is to provide a biodegradable polyacrylonitrile-based carbon fiber and its preparation method, thereby solving the problems of long degradation cycles and uncontrollable degradation rates in existing biodegradable carbon fibers.

[0005] In a first aspect, this application provides a method for preparing biodegradable polyacrylonitrile-based carbon fiber, comprising the following steps: Acrylonitrile and ester-containing functional monomers are copolymerized to obtain a spinning solution; Polyacrylonitrile precursor fibers were obtained by spinning the spinning solution. The polyacrylonitrile precursor fibers were subjected to pre-oxidation treatment, carbonization treatment, and surface activation treatment with hydrogen peroxide in sequence to obtain biodegradable polyacrylonitrile-based carbon fibers.

[0006] In the above technical solution, this application copolymerizes acrylonitrile and ester-containing functional monomers to introduce degradable ester bonds into the PAN molecular chain, constructing hydrolyzable breaking points, enabling carbon fibers to simultaneously achieve high strength and degradability. Then, after pyrolysis, surface activation treatment with hydrogen peroxide is performed to etch micropores onto the fiber surface and selectively oxidize the fiber surface to form carboxyl groups. The surface carboxyl groups, as polar groups, can adsorb water molecules that enter the fiber core through the micropores, attacking the ester bonds inside the fiber, thereby achieving overall, uniform, and rapid degradation, rather than slow surface erosion, effectively shortening the degradation cycle of the carbon fiber. Furthermore, by controlling the ester-containing functional monomers (e.g., type or amount), the number of degradation sites in the copolymer molecular chain can be controlled accordingly; and by controlling the surface activation process, the carboxyl content and surface microporous structure can be adjusted accordingly, achieving a controllable degradation rate. This preparation method is simple to operate, with controllable reaction conditions, and produces degradable polyacrylonitrile-based carbon fibers with high strength, short degradation cycle, and controllable degradation rate.

[0007] In some embodiments of this application, the functional monomer includes at least one of hydroxyethyl methacrylate and dimethyl itaconic acid. In some embodiments of this application, the mass percentage of the functional monomer is 5wt% to 15wt% based on the total mass of the monomers in the copolymerization reaction. In some embodiments of this application, before spinning the spinning solution, the method further includes mixing the spinning solution with carbon nanotubes. Preferably, the carbon nanotubes include carboxylated carbon nanotubes. Preferably, the mass of the carbon nanotubes accounts for 0.3wt% to 0.5wt% of the mass of the spinning solution. In some embodiments of this application, the spinning method is dry-jet wet spinning. In some embodiments of this application, the method for preparing the spinning solution includes: copolymerizing acrylonitrile, functional monomers, and initiators in an ionic liquid solvent.

[0008] In some embodiments of this application, the copolymerization reaction temperature is 50°C to 70°C and the time is 10h to 14h. In some embodiments of this application, the ionic liquid includes at least one of 1-butyl-3-methylimidazolium chloride or 1-ethyl-3-methylimidazolium acetate.

[0009] In some embodiments of this application, the initiator includes at least one of azobisisobutyronitrile, dimethyl azobisisobutyrate, or 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone.

[0010] In some embodiments of this application, the copolymerization reaction further includes: removing monomers and bubbles from the spinning solution to obtain a homogeneous spinning solution.

[0011] In some embodiments of this application, the surface activation treatment includes: treating the carbonized fibers after carbonization at 300°C to 350°C with hydrogen peroxide vapor. Preferably, the concentration of hydrogen peroxide vapor is 25 vol% to 35 vol%, the flow rate of the carrier gas is 0.3 L / min to 1.0 L / min, and the treatment time is 5 min to 15 min.

[0012] In some embodiments of this application, after surface activation treatment, the method further includes: ultrasonically treating the activated fibers obtained after surface activation treatment in a sodium hydroxide solution. Preferably, the concentration of the sodium hydroxide solution is 0.1 mol / L to 0.5 mol / L. Preferably, the ultrasonic treatment time is 5 min to 10 min.

[0013] In some embodiments of this application, the pre-oxidation treatment is carried out at 145°C to 220°C for 60 min to 120 min. Preferably, the pre-oxidation treatment is carried out in an air atmosphere with a heating rate ≤1°C / min.

[0014] In some embodiments of this application, the pre-oxidation treatment includes: passing polyacrylonitrile precursor fibers sequentially through a first pre-oxidation temperature zone, a second pre-oxidation temperature zone, and a third pre-oxidation temperature zone; wherein the temperature of the first pre-oxidation temperature zone is 145℃~155℃, and the residence time is 25min~35min; the temperature of the second pre-oxidation temperature zone is 175℃~185℃, and the residence time is 25min~35min; and the temperature of the third pre-oxidation temperature zone is 200℃~220℃, and the residence time is 25min~35min.

[0015] In some embodiments of this application, the carbonization treatment temperature is 600℃~800℃, and the time is 25min~35min. Preferably, the carbonization treatment is carried out under an inert atmosphere, and the heating rate is ≤5℃ / min.

[0016] Secondly, embodiments of this application provide a biodegradable polyacrylonitrile-based carbon fiber, which is prepared by the above-described preparation method.

[0017] In the above technical solution, the biodegradable polyacrylonitrile-based carbon fiber of this application introduces biodegradable ester group sites into the molecular chain, and has carboxyl groups on the fiber surface. Micropores are formed on the fiber surface and inside the fiber, maintaining high strength while exhibiting a short degradation cycle and a controllable degradation rate. Under conditions of pH 12 and 60℃, the degradation rate of this biodegradable polyacrylonitrile-based carbon fiber is ≥85% after 30 days, and the degradation products are succinic acid / acrylic acid.

[0018] Thirdly, this application also provides an application of biodegradable polyacrylonitrile-based carbon fiber, which is used to prepare wind turbine blades, bone repair devices, or antistatic packaging materials. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a process flow diagram of a method for preparing biodegradable polyacrylonitrile-based carbon fiber provided in an embodiment of this application.

[0021] Figure 2 This is a scanning electron microscope cross-section image of the biodegradable polyacrylonitrile-based carbon fiber in Example 1 of this application after 5 days of degradation at 5000 magnification.

[0022] Figure 3 This is a scanning electron microscope cross-section image of the polyacrylonitrile-based carbon fiber in Comparative Example 1 of this application after 5 days of degradation at 5000 magnification. Detailed Implementation

[0023] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the biodegradable polyacrylonitrile-based carbon fiber, its preparation method, and its applications, but some unnecessary details may be omitted.

[0024] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is expected that the ranges 60~110 and 80~120 will also be understood.

[0025] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions. Unless otherwise specified, all steps of this application can be performed sequentially or randomly, preferably sequentially.

[0026] Figure 1This is a process flow diagram illustrating a method for preparing biodegradable polyacrylonitrile-based carbon fiber, provided in an embodiment of this application. Please refer to [link / reference]. Figure 1 The method for preparing biodegradable polyacrylonitrile-based carbon fiber provided in this application includes the following steps: S1, acrylonitrile and ester-containing functional monomers are copolymerized to obtain spinning solution.

[0027] In this application, "ester-containing functional monomers" refers to compounds whose molecular structure contains both ester groups (-COO-) and polymerizable functional groups (such as carbon-carbon double bonds, triple bonds, etc.).

[0028] In some embodiments, the functional monomers include at least one of hydroxyethyl methacrylate and dimethyl itaconic acid. The hydroxyl functional groups provided by hydroxyethyl methacrylate not only enhance the hydrophilicity of the copolymer to accelerate hydrolysis, but their hydrogen bonding with the PAN backbone also effectively inhibits phase separation, ensuring the mechanical properties of the carbon fibers. Dimethyl itaconic acid, due to its diester structure, provides a high density of degradation sites, which is beneficial for further increasing the degradation rate. In some embodiments, the functional monomers account for 5 wt% to 15 wt% of the total mass of the monomers in the copolymerization reaction. By controlling the amount of functional monomers added within an appropriate range, it is beneficial to introduce more degradation sites, thereby increasing the degradation rate while maintaining appropriate mechanical strength of the carbon fibers. As an example, the mass percentage of the functional monomer is within any two values ​​of 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, or more. In some embodiments, the method for preparing the spinning solution includes: copolymerizing acrylonitrile, functional monomers, and an initiator in an ionic liquid solvent. Using an ionic liquid solvent helps to prevent premature hydrolysis of the ester groups, thereby ensuring a uniform molecular weight distribution of the copolymer.

[0029] In some embodiments, the copolymerization reaction temperature is 50°C to 70°C, and the time is 10h to 14h. As an example, the copolymerization reaction temperature is a range between any two values ​​of 50°C, 55°C, 60°C, 65°C, 70°C, or above; and the time is a range between any two values ​​of 10h, 11h, 12h, 13h, 14h, or above. In some embodiments, the ionic liquid includes at least one of 1-butyl-3-methylimidazolium chloride or 1-ethyl-3-methylimidazolium acetate.

[0030] In some embodiments, the initiator includes at least one of azobisisobutyronitrile, dimethyl azobisisobutyrate, or 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone. In some embodiments, after the copolymerization reaction, the method further includes: performing desing and defoaming treatment on the spinning solution to obtain a homogeneous spinning solution.

[0031] The demonstration and debubbling processes involve: the spinning solution is fed into a demonstration vessel to remove unreacted acrylonitrile, and then fed into a debubbling vessel to remove bubbles. Through precise control of the demonstration and debubbling processes, high-quality homogeneous polymerization solutions can be obtained to the maximum extent, while reducing gels and impurities that contribute to defects in the precursor fiber structure.

[0032] S2, the spinning solution is spun to obtain polyacrylonitrile precursor fiber.

[0033] In some embodiments, the spinning process can be wet spinning or dry-jet wet spinning. Preferably, the spinning process is dry-jet wet spinning. The fiber precursor produced by dry-jet wet spinning has a smooth surface and few defects, which is the basis for high-strength carbon fibers.

[0034] Specifically, the spinning solution can be spun using a dry-spray wet forming process, and polyacrylonitrile precursor fibers can be obtained by sequentially going through processes such as water washing, hot water drawing, drying, steam drawing, and oiling.

[0035] In some embodiments, before spinning the spinning solution, the method further includes mixing the spinning solution with carbon nanotubes.

[0036] Carbon nanotubes (CNTs) possess extremely high intrinsic strength and modulus. When dispersed within a PAN matrix, they form a three-dimensional network that effectively bears externally applied loads and reduces stress concentration. Furthermore, the interfacial bonding between CNTs and PAN molecular chains transfers stress from the weaker polymer matrix to the stronger CNTs, thus delaying fiber fracture. Additionally, when microcracks appear in the fibers, uniformly dispersed CNTs act as barriers, forcing crack tips to deflect or bypass them, effectively preventing crack propagation and improving the material's toughness and strength. Moreover, on the one-dimensional nanoscale surface of CNTs, PAN molecular chains, due to their polarity and interactions, more readily align and crystallize along the long axis of the CNTs, reducing random entanglement of molecular chains. In short, the addition of carbon nanotubes can effectively improve the mechanical properties of biodegradable carbon fibers.

[0037] Preferably, the carbon nanotubes include carboxylated carbon nanotubes. Further selection of carboxylated carbon nanotubes is preferred, as the carboxyl functional groups exhibit strong polar interactions with the cyano groups on the PAN molecular chain, potentially even forming hydrogen bonds (OH···N≡C). This strong interfacial bonding is a prerequisite for effective stress transfer. Furthermore, carboxylation imparts a polar surface to the CNTs, improving their compatibility with polar solvents (such as ionic liquids) and PAN, which is beneficial for further enhancing the mechanical properties of biodegradable carbon fibers.

[0038] Understandably, carboxylated carbon nanotubes can be purchased directly or prepared using conventional methods in the art. As an example, multi-walled or single-walled carbon nanotubes can be treated with sulfuric acid or nitric acid. Preferably, the mass of carbon nanotubes accounts for 0.3wt% to 0.5wt% of the mass of the spinning solution. As an example, the mass of carbon nanotubes accounts for any two values ​​between 0.3wt%, 0.35wt%, 0.45wt%, 0.5wt%, 0.5wt%, or more of the mass of the spinning solution.

[0039] S3 involves sequentially pre-oxidizing, carbonizing, and surface-activating polyacrylonitrile precursor fibers with hydrogen peroxide to obtain biodegradable polyacrylonitrile-based carbon fibers.

[0040] In some embodiments, the pre-oxidation treatment is carried out at 145°C to 220°C for 60 min to 120 min. Preferably, the pre-oxidation treatment is carried out in an air atmosphere with a heating rate ≤1°C / min.

[0041] By controlling the conditions of the pre-oxidation treatment, low-temperature cyclization can be achieved while protecting the ester groups from decomposition.

[0042] Further, the pre-oxidation treatment includes: passing the polyacrylonitrile precursor fiber sequentially through a first pre-oxidation temperature zone, a second pre-oxidation temperature zone, and a third pre-oxidation temperature zone; wherein, the temperature of the first pre-oxidation temperature zone is 145℃~155℃, and the residence time is 25min~35min; the temperature of the second pre-oxidation temperature zone is 175℃~185℃, and the residence time is 25min~35min; the temperature of the third pre-oxidation temperature zone is 200℃~220℃, and the residence time is 25min~35min.

[0043] As an example, the temperature of the first pre-oxidation zone is 150°C and the residence time is 30 min; the temperature of the second pre-oxidation zone is 180°C and the residence time is 30 min; and the temperature of the third pre-oxidation zone is 220°C and the residence time is 30 min.

[0044] In some embodiments, the carbonization temperature is 600°C to 800°C, and the time is 25 min to 35 min. As an example, the carbonization temperature is within the range of any two values ​​of 600°C, 650°C, 700°C, 750°C, 800°C, or higher; and the time is within the range of any two values ​​of 25 min, 30 min, 35 min, or higher.

[0045] Preferably, the carbonization process is carried out under an inert atmosphere with a heating rate ≤ 5°C / min. As an example, the carbonization process is carried out under a nitrogen atmosphere with a heating rate of 5°C / min.

[0046] In some embodiments, the surface activation treatment includes subjecting the carbonized fibers after carbonization to hydrogen peroxide (H2O2) vapor treatment at 300°C to 350°C. As an example, the temperature of the surface activation treatment can be any two values ​​between 300°C, 310°C, 320°C, 330°C, 340°C, and 350°C.

[0047] H2O2 vapor decomposes at around 300℃ to produce hydroxyl radicals, which can etch amorphous carbon on the fiber surface to form micropores. At the same time, it selectively oxidizes active groups (such as hydroxyl groups) on the carbon fiber surface to form carboxyl groups. Furthermore, compared to liquid H2O2, H2O2 vapor is more conducive to uniform diffusion and penetration, and the reaction temperature helps to reduce side reactions.

[0048] Preferably, the concentration of H2O2 vapor is 25 vol% to 35 vol%, the flow rate of the carrier gas is 0.3 L / min to 1.0 L / min, and the treatment time is 5 min to 15 min. As an example, the concentration of H2O2 vapor is within the range of any two values ​​between 25 vol%, 30 vol%, and 35 vol% or higher; the flow rate of the carrier gas N2 is within the range of any two values ​​between 0.3 L / min, 0.5 L / min, 0.7 L / min, and 1.0 L / min; and the treatment time is within the range of any two values ​​between 5 min, 8 min, 10 min, 12 min, and 15 min.

[0049] In some embodiments, after surface activation treatment, the method further includes: ultrasonically treating the activated fibers obtained after surface activation treatment in a sodium hydroxide solution.

[0050] On the one hand, ester-bonded functional monomers (such as hydroxyethyl methacrylate) embedded within the fiber serve as pre-defined degradation sites. OH⁻ ions provided by sodium hydroxide (NaOH) solution attack these ester bonds, causing hydrolysis. This process preferentially occurs near existing micropores within the fiber, expanding and deepening these channels, thus further promoting degradation. On the other hand, surface carboxyl groups generated by hydrogen peroxide activation react with NaOH to form more hydrophilic sodium carboxylate salts. This reaction significantly increases the hydrophilicity of the fiber surface, allowing for faster absorption and penetration of the aqueous solution during subsequent degradation. Furthermore, ultrasonic treatment generates a cavitation effect in the liquid (forming microbubbles and violently bursting), producing extremely strong localized shock waves and microjets. This cleans and unblocks the channels, mechanically expanding existing micropores, promoting reagent diffusion, and ultimately forming unobstructed, hydrophilic, high-speed degradation channels. Therefore, the degradation medium can rapidly penetrate the fiber interior, simultaneously attacking numerous ester bonds, achieving rapid and uniform overall degradation, rather than a slow, surface-to-interior degradation process.

[0051] Preferably, the concentration of the sodium hydroxide solution is 0.1 mol / L to 0.5 mol / L. As an example, the concentration of the sodium hydroxide solution is 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, or any two of the above values.

[0052] Preferably, the ultrasonic treatment time is 5 min to 10 min. As an example, the ultrasonic treatment time is within the range of any two values ​​of 5 min, 6 min, 7 min, 8 min, 9 min, 10 min or more.

[0053] Understandably, surface activation treatment also includes surface treatment of the carbonized fibers and some other post-treatment processes.

[0054] The surface treatment can be achieved using conventional electrochemical anodizing. Other post-treatment processes may include washing, sizing, drying, and winding.

[0055] This application introduces degradable ester bonds into the PAN molecular chain by copolymerizing acrylonitrile and ester-containing functional monomers, constructing hydrolytic breakage points that allow carbon fibers to maintain high strength while possessing degradable properties. Then, surface activation treatment with hydrogen peroxide is performed after pyrolysis, etching the fiber surface to create micropores and selectively oxidizing the fiber surface to form carboxyl groups. The presence of micropores effectively increases the contact area between the carbon fiber and the degradation environment, allowing the degradation reaction to occur simultaneously within the fiber, rather than being limited to the surface. The surface carboxyl groups, as polar groups, can adsorb water molecules that enter the fiber core through the micropores, attacking the ester bonds within the fiber, thus achieving a holistic, uniform, and rapid breakdown rather than slow surface erosion, effectively shortening the carbon fiber degradation cycle. Furthermore, the carboxyl groups have a catalytic effect on the hydrolysis of ester bonds, accelerating the breakage rate of adjacent ester bonds, i.e., accelerating degradation. Moreover, the presence of these surface carboxyl groups has almost no impact on the high-strength carbon skeleton of the fiber core, meaning it does not reduce the fiber's mechanical properties, but only plays a role in the degradation environment. Compared to the traditional layer-by-layer degradation model from the outside in, which is slow and the degradation rate is uncontrollable, the biodegradable polyacrylonitrile-based carbon fiber prepared in this application can achieve degradation "from the inside out", thereby effectively accelerating the degradation rate and shortening the degradation cycle.

[0056] Furthermore, the higher the monomer content and / or the more ester groups in the monomer, the more degradation sites are formed. By controlling the functional monomers containing ester groups (e.g., type or amount), the number of degradation sites in the copolymer molecular chain can be controlled accordingly. Controlling the surface activation process (e.g., temperature, time, hydrogen peroxide concentration) can correspondingly control the carboxyl content and surface microporous structure (pore size and density), thus achieving a controllable degradation rate. This preparation method is simple to operate, with controllable reaction conditions. The resulting biodegradable polyacrylonitrile-based carbon fibers have high strength, a short degradation cycle, and a controllable degradation rate, allowing for control of the degradation reaction process and avoiding unpredictable disintegration.

[0057] In addition, this application also provides a biodegradable polyacrylonitrile-based carbon fiber prepared by the above preparation method.

[0058] The biodegradable polyacrylonitrile-based carbon fiber of this application introduces biodegradable ester sites into the molecular chain, and has carboxyl groups on the fiber surface. Micropores are formed on the fiber surface and inside the fiber, maintaining high strength while exhibiting a short degradation cycle and a controllable degradation rate. Under conditions of pH 12 and 60℃, the biodegradable polyacrylonitrile-based carbon fiber achieves a degradation rate of ≥85% after 30 days, with the degradation products being succinic acid / acrylic acid.

[0059] In addition, this application also provides an application of biodegradable polyacrylonitrile-based carbon fiber, which is used to prepare wind turbine blades, bone repair devices or antistatic packaging materials.

[0060] As an example, this biodegradable polyacrylonitrile-based carbon fiber was used to prepare a reinforcing skeleton for wind turbine blades, which can be degraded and recycled through an alkaline solution after its service life.

[0061] As an example, this biodegradable polyacrylonitrile-based carbon fiber was used to prepare absorbable bone repair devices, achieving controlled degradation in vivo over 3 to 6 months.

[0062] As an example, when this biodegradable polyacrylonitrile-based carbon fiber was used to prepare antistatic packaging materials, the mass loss was ≥80% after 12 weeks under composting conditions.

[0063] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0064] Example 1 This embodiment provides a biodegradable polyacrylonitrile-based carbon fiber, the preparation method of which includes the following steps: (1) Copolymerization reaction Using 1-butyl-3-methylimidazolium acetate as solvent and azobisisobutyronitrile as initiator, hydroxyethyl methacrylate and acrylonitrile were mixed at a mass ratio of 1:9 and copolymerized in a polymerization reactor at 60°C for 12 hours to obtain a spinning solution with a solid content of 17%. The spinning solution was then directly transferred to a de-acrylonitrile reactor to remove unreacted acrylonitrile, and finally transferred to a degassing reactor to remove air bubbles, resulting in a homogeneous spinning solution with a solid content of 18%.

[0065] (2) Spinning The homogeneous spinning solution was thoroughly mixed with 0.5 wt% carboxylated carbon nanotubes, and then spun using dry-jet wet spinning technology to obtain PAN precursor fibers.

[0066] (3) Pre-oxidation treatment The aforementioned polyacrylonitrile precursor fibers were sequentially subjected to pre-oxidation treatment in a first pre-oxidation temperature zone, a second pre-oxidation temperature zone, and a third pre-oxidation temperature zone. The temperature in the first pre-oxidation temperature zone was 150℃, and the residence time was 30 minutes; the temperature in the second pre-oxidation temperature zone was 180℃, and the residence time was 30 minutes; the temperature in the third pre-oxidation temperature zone was 220℃, and the residence time was 30 minutes, thus obtaining pre-oxidized polyacrylonitrile fibers.

[0067] (4) Carbonization treatment The PAN pre-oxidized fiber was passed into a low-temperature carbonization furnace with nitrogen as the protective gas and the temperature increased to 800°C at a rate of 5°C / min, and held for 30 minutes.

[0068] (5) Surface activation treatment 30 vol% H2O2 steam (with a N2 flow rate of 0.5 L / min) was introduced into the carbonization furnace and treated at 300 °C for 10 min.

[0069] Example 2 This embodiment provides a biodegradable polyacrylonitrile-based carbon fiber, the preparation method of which differs from that of Example 1 in that: In step (1), dimethyl itaconic acid is used instead of hydroxyethyl methacrylate, and the mass ratio of dimethyl itaconic acid to acrylonitrile is 1:9.

[0070] Example 3 This embodiment provides a biodegradable polyacrylonitrile-based carbon fiber, the preparation method of which differs from that of Example 1 in that it further includes: (6) Ultrasonic treatment The activated fibers obtained after surface activation treatment were ultrasonically treated in a 0.2 mol / L sodium hydroxide solution for 10 min, then washed with water and dried to obtain biodegradable polyacrylonitrile-based carbon fibers.

[0071] Example 4 This embodiment provides a biodegradable polyacrylonitrile-based carbon fiber, the preparation method of which differs from that of Example 1 in that: Step (5) includes: introducing 25 vol% H2O2 steam (with a N2 flow rate of 0.8 L / min) into the carbonization furnace and treating it at 350°C for 5 min. Comparative Example 1 This comparative example provides a polyacrylonitrile-based carbon fiber, the preparation method of which differs from that of Example 1 in that: hydroxyethyl methacrylate is not added in step (1) and step (5) is not included.

[0072] Comparative Example 2 This comparative example provides a polyacrylonitrile-based carbon fiber, the preparation method of which differs from that of Example 1 in that step (5) is not included.

[0073] Comparative Example 3 This comparative example provides a polyacrylonitrile-based carbon fiber, the preparation method of which differs from that of Example 1 in that hydroxyethyl methacrylate is replaced with itaconic acid in step (1).

[0074] The preparation parameters of some polyacrylonitrile-based carbon fibers in the above embodiments and comparative examples are shown in Table 1.

[0075] Table 1. Some preparation parameters of polyacrylonitrile-based carbon fibers

[0076] Test case The thermal cross-sectional morphology and degradation rate of the polyacrylonitrile-based carbon fibers prepared in the examples and comparative examples were tested, and the tensile strength of the polyacrylonitrile-based carbon fibers was also tested. The specific test methods are as follows: (1) Cross-sectional morphology: The dried polyacrylonitrile-based carbon fibers were broken into brittle fragments and fixed onto a cylindrical sample holder with an appropriate amount of conductive adhesive. The carbon fibers were sputtered with gold using an ion sputtering instrument with a current controlled at 12 μA and a duration of 70 s before SEM testing.

[0077] (2) Degradation rate: Polyacrylonitrile-based carbon fiber was cut into segments, vacuum dried to constant weight and weighed, and recorded as M0; it was immersed in a buffer solution with pH 12, and subjected to constant temperature shaking water bath (60℃) for 5 groups of equilibrium experiments. After removal, the reaction was terminated with a buffer solution with pH 7, and freeze-dried (-50℃, 48h) to constant weight, and weighed Wt.

[0078] Degradation rate = (M0 - Wt) ÷ M0 × 100% (3) Tensile strength: Tested according to GB / T3362 test standard.

[0079] The performance test results are shown in Table 2 and Figure 2 and Figure 3.

[0080] Table 2. Performance test results of polyacrylonitrile-based carbon fibers in the examples and comparative examples.

[0081] As shown in Table 2, compared with Comparative Examples 1 to 3, the polyacrylonitrile-based carbon fibers prepared in Examples 1 to 4 of this application maintain high strength while exhibiting a higher degradation rate and a shorter degradation cycle. These biodegradable polyacrylonitrile-based carbon fibers have a tensile strength of not less than 4.0 GPa, and under conditions of pH 12 and 60°C, the degradation rate after 30 days is greater than 80%, reaching a maximum of 90.2%.

[0082] A comparison of Examples 1, 2, and 4 shows that the degradation cycle and degradation rate can be synergistically controlled by adjusting the type of functional monomer and the surface activation treatment conditions.

[0083] Figure 2 This is a scanning electron microscope cross-section image of the biodegradable polyacrylonitrile-based carbon fiber in Example 1 of this application after 5 days of degradation at 5000 magnification. Figure 3 This is a scanning electron microscope (SEM) cross-sectional image of the polyacrylonitrile-based carbon fiber in Comparative Example 1 of this application after 5 days of degradation at 5000 magnification. (See Table 2 for details.) Figure 2 , Figure 3 It can be seen that, compared with Comparative Example 1, the polyacrylonitrile-based carbon fiber in Example 1 exhibits increased cross-sectional defects under the degradation environment, while the polyacrylonitrile-based carbon fiber in Comparative Example 1 does not degrade and has a smooth, defect-free cross-section. Correspondingly, the degradation rate of the polyacrylonitrile-based carbon fiber in Comparative Example 1 is only 4.6% after 30 days.

[0084] As can be seen from Example 1 and Comparative Examples 2 and 3, the hydrogen peroxide surface activation treatment combined with functional monomer type control in this application can effectively improve the degradation rate and shorten the degradation cycle while maintaining an appropriate strength.

[0085] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A method for preparing biodegradable polyacrylonitrile-based carbon fiber, characterized in that, Includes the following steps: Acrylonitrile and ester-containing functional monomers are copolymerized to obtain a spinning solution; The spinning solution is used to spin polyacrylonitrile precursor fiber; The polyacrylonitrile precursor fiber was subjected to pre-oxidation treatment, carbonization treatment, and surface activation treatment with hydrogen peroxide in sequence to obtain biodegradable polyacrylonitrile-based carbon fiber.

2. The preparation method according to claim 1, characterized in that, The functional monomer includes at least one of hydroxyethyl methacrylate and dimethyl itaconic acid. And / or, based on the total mass of the monomers in the copolymerization reaction, the mass percentage of the functional monomers is 5wt% to 15wt%.

3. The preparation method according to claim 1, characterized in that, Before spinning the spinning solution, the method further includes: mixing the spinning solution with carbon nanotubes; Preferably, the carbon nanotubes include carboxylated carbon nanotubes; Preferably, the carbon nanotubes account for 0.3wt% to 0.5wt% of the mass of the spinning solution. Preferably, the spinning method is dry-jet wet spinning.

4. The preparation method according to claim 1, characterized in that, The method for preparing the spinning solution includes: copolymerizing the acrylonitrile, the functional monomer, and the initiator in an ionic liquid solvent; Preferably, the copolymerization reaction is carried out at a temperature of 50°C to 70°C for 10 to 14 hours. Preferably, the ionic liquid comprises at least one of 1-butyl-3-methylimidazolium chloride or 1-ethyl-3-methylimidazolium acetate; Preferably, the initiator includes at least one selected from azobisisobutyronitrile, dimethyl azobisisobutyrate, or 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone; Preferably, after the copolymerization reaction, the process further includes: removing monomers and defoaming the spinning solution.

5. The preparation method according to claim 1, characterized in that, The surface activation treatment includes: treating the carbonized fibers after carbonization at 300℃~350℃ with hydrogen peroxide vapor. Preferably, the concentration of hydrogen peroxide vapor is 25 vol% to 35 vol%, the flow rate of the carrier gas is 0.3 L / min to 1.0 L / min, and the treatment time is 5 min to 15 min.

6. The preparation method according to claim 1, characterized in that, The surface activation treatment further includes: ultrasonically treating the activated fibers obtained after the surface activation treatment in a sodium hydroxide solution; Preferably, the concentration of the sodium hydroxide solution is 0.1 mol / L to 0.5 mol / L; Preferably, the ultrasonic treatment time is 5 min to 10 min.

7. The preparation method according to claim 1, characterized in that, The pre-oxidation treatment is carried out at 145℃~220℃ for 60min~120min. Preferably, the pre-oxidation treatment is carried out in an air atmosphere, with a heating rate ≤1℃ / min; Preferably, the pre-oxidation treatment includes: passing the polyacrylonitrile precursor fiber sequentially through a first pre-oxidation temperature zone, a second pre-oxidation temperature zone, and a third pre-oxidation temperature zone; wherein the temperature of the first pre-oxidation temperature zone is 145℃~155℃, and the residence time is 25min~35min; the temperature of the second pre-oxidation temperature zone is 175℃~185℃, and the residence time is 25min~35min; and the temperature of the third pre-oxidation temperature zone is 200℃~220℃, and the residence time is 25min~35min.

8. The preparation method according to claim 1 or 7, characterized in that, The carbonization treatment is carried out at a temperature of 600℃~800℃ for a time of 25min~35min; Preferably, the carbonization process is carried out under an inert atmosphere, with a heating rate ≤ 5℃ / min.

9. A biodegradable polyacrylonitrile-based carbon fiber, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 8.

10. An application of the biodegradable polyacrylonitrile-based carbon fiber as described in claim 9, characterized in that, The biodegradable polyacrylonitrile-based carbon fiber can be used to prepare wind turbine blades, bone repair devices, or antistatic packaging materials.

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